This stands for Interesting People On The Road. I was calling them Idiots On The Road (I.O.T.R.s)...but that sounded a bit harsh. Though sometimes when people make interesting, last minute, your heart has fallen into your lap, swerves in the road...or cut you off on the road...the word "idiot" does come to mind. Though I do recall a couple of times when people must have thought the same of me...though I must say that 99% of the time I really am a careful driver.
I encountered about 12 of them on my travels yesterday.
Ah well. They probably didn't realize. That is what I am hoping... I know for sure that the two times I can recall that I did that, I did not realize.